The invention relates to a vibratory parts feeder utilizing an electromagnetic vibratory drive. Particularly, the invention relates to an improvement in the electromagnetic drive and an improvement in the base assembly which supports the electromagnet of the drive.
A typical vibratory parts feeder is shown in U.S. Pat. No. 3,258,111. The feeder includes a base mass that is supported upon vibration isolators and a frame mass that is mounted above the base mass by four inclined leaf spring sets which enable rotational oscillatory movement of the frame mass in response to an exciter motor. The frame mass includes a bowl for receiving parts.
The exciter motor is of an electromagnetic type that includes a field core and a coil mounted on the base mass. An armature is mounted on the underside of the frame mass with an air gap between opposing facing of the field core legs and the armature. When an alternating current is supplied to the coil, the armature and frame mass are alternately drawn toward the coil and released, flexing the leaf spring sets. Thus, the frame mass oscillates rotationally about a central vertical axis at a predetermined frequency that is established by the frequency of the current supplied to the coil.
As described for example in U.S. Pat. No. 4,007,825, a helical track originates in the bottom of the bowl and extends upwardly along an inner periphery of the bowl wall to an exit station at the top of the bowl. Parts can be progressively fed from the lower portion of the bowl along the helical track to the exit station as a given feed rate by vibratory energy.
Many manufacturers in the industry operate the vibratory bowl units at their resonant frequency to minimize electrical power consumption and to achieve maximum vibratory stroke. The pitfall of this approach is that the bowls and drives are then sensitized to mass changes, caused by more or fewer parts contained in the bowl, which creates increases and decreases in the vibratory stroke corresponding to the mass changes. A known solution to this pitfall has been to design sophisticated, and somewhat expensive, controls which monitor the resonant frequency and amplitude of stroke, and using these parameters, to change the control output dynamically to maintain the desired amplitude of vibration. This also has been a relatively expensive solution.
The present invention provides an electromagnet and armature mounting configuration that allows for optimization of the electromagnetic flux field density created by the electromagnetic coil. The configuration of the mounting allows for enhanced power conversion from electromagnetic power to physical bowl movement in the vibratory direction desired. Because of this approach, heavier vibratory bowls can be excited with less required electrical energy than units currently available.
According to one aspect of the invention, the electromagnet and armature are intentionally misaligned across the magnetic gap. By mis-aligning the armature to the electromagnet across the magnetic gap, the direct lines of magnetic force can be adjusted to fine tune the driving force of the vibratory drive and the natural frequency of the drive to adjust vibratory amplitude. The common industry practice is to align the magnet core and armature faces, in a direct alignment, to capitalize on the straight line of force attraction between the magnet core and the armature.
According to another aspect of the invention, the magnet core and a magnetic armature are rotationally misaligned such that the magnetic force will exert both an attractive force between the magnet core and the armature and a relative torque between the magnet core and the armature tending to align the poles of the armature and the magnetic core. This torque is arranged to be additive to the rotary force caused by the deflection of the inclined springs caused by the attractive force between the magnet core and the armature.
The invention allows for the adjustability of magnet core and armature alignment to modify bowl vibration amplitude. The unit may be aligned directly or can be misaligned dependent on the application desired. By intentionally mis-aligning the magnet core and the armature, advantages can be achieved such as the use of a single magnet on larger drive units, the xe2x80x9cdrive unitxe2x80x9d being the parts feeder less the bowl; the use of only three spring stacks on larger units where such units typically have four or more spring stacks; significantly decreased power consumption while maintaining vibrational power. In some cases, a reduction by a factor of five for similar performance can be achieved. The invention allows for simple control technology to maintain higher strokes, such as by using variable voltage with no amplitude feedback.
The invention allows a single drive unit to handle a wide range of bowl weights such that one drive unit can be adjusted to carry a range of bowl sizes. Significantly lower inventory and manufacturing costs can be achieved.
The achievement of maximum stroke and minimization of electrical power consumption are achieved by operating the unit, not at resonance, but at a point above or below resonance to allow for mass changes in the bowl load which will then not affect the amplitude of the vibratory stroke.
According to another aspect of the invention, amplitude adjustment can be controlled by adding counterweight to the drive unit versus changing the springs to tune the resonant frequency of the unit. The manufacturing time to tune a parts feeder is greatly reduced. The invention utilizes a round baseplate design which allows the unit to be simply enclosed for aesthetic or for potential air purging applications. The counterweights have a ring segment shape to compactly fit on the round baseplate. The desired mass 1 (base assembly and electromagnet) to mass 2 (bowl, frame and armature) ratio can be maintained by increasing the mass 1 using incremental weight counterweights bolted to a common baseplate design. Manufacturing economies of scale can thus be achieved. The invention allows for the manufacture of one size of base assembly to replace a product mix of five sizes.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.